1. Field of the Invention
The present invention relates to a construction of a transmission adapted to a working vehicle like a tractor for transmitting power from an engine of the vehicle into a differential unit for rear wheels thereof, particularly, of a type having a travelling-input shaft drivingly connected with the engine and a travelling-output shaft drivingly connected with the differential unit, which are disposed in parallel to each other, and it relates to a construction of a housing for the transmission. Additionally, it relates to various systems in connection with the transmission, particularly, a speed-changing operation system (occasionally having a creeping speed range), which includes a supporting mechanism of a lever for speed-changing and a connecting and disconnecting mechanism of the speed-changing operation system to the transmission.
2. Related Art
A transmission of a working vehicle like a tractor includes a series of a main-clutch system and a speed-changing system between an output area of an engine mounted on a front portion of the vehicle and a differential unit for rear wheels housed in a rear axle housing supporting rear axles. Conventionally, the main-clutch system is housed in a clutch housing as a front part housing continuously connected to the output portion of the engine, and the speed-changing system is housed in an exclusive transmission casing as a middle part housing interposed between the front part housing and the rear axle housing as a rear part housing. The transmission casing is fastened at its front and rear ends to both of the housings by bolts. The main-clutch system and the speed-changing system are connected with each other according to fastening the clutch housing and the transmission casing.
Also, the conventional speed-changing system housed in the transmission casing has reversing arrangement and tandem speed-changing arrangements distributively disposed on a shaft as described in Japanese Patent No. Hei 5-26686.
Also, the conventional transmission casing has respective supporting portions for a plurality of speed-changing levers as described in Japanese Utility Model No. Hei 6-3213.
Japanese Patent Nos. Hei 5-26686 and Hei 7-117507 describe a front-wheel driving PTO (power-take off) system for transmitting power from the speed-changing system in the transmission casing to the front wheels. Particularly, the former describes a front-wheel driving PTO unit outwardly projecting from the transmission casing. A transmission shaft connecting the unit and the speed-changing system is disposed outside the transmission casing.
It is desirable to reduce the manufacturing cost of the transmission and to simplify its assembly and maintenance. However, the conventional housing for the transmission consists of the above-mentioned three part housings fastened together by bolts, thereby requiring two processes of positioning and bolting to fasten them. Thus, it is complicated and expensive to assemble the housing.
It is conceivable for a single housing member to replace the front and middle part housings. In this way, only a process of fastening the single housing member and the rear axle housing is required to manufacture a housing for the transmission. However, the main-clutch system and the speed-changing system must be housed in the housing member, wherein each of the systems requires to be settled easily and supported steadily.
Referring to the conventional speed-changing lever, the supporting portions for the lever are formed integrally with the transmission casing, thereby complicating manufacture of the transmission casing and increasing its price, especially when a plurality of supporting portions are formed in correspondence to a plurality of levers.
Referring to the conventional front-wheel driving PTO system, the unit therefor is partly housed in the transmission casing so as to be disposed at a longitudinally intermediate space of the speed-changing system or at a rear space, whereby the distance between the unit and the front-wheel driving unit disposed between left and right front wheels is long. Thus, the transmission shaft between both of the units must be long, thereby causing a high manufacturing cost and lowering the efficiency of front-wheel driving. Therefore it is desirable for the front-wheel driving PTO unit to be near the front-wheel driving unit.
The transmission shown in Japanese Patent No. Hei 5-26686 is constructed between a travelling-input shaft drivingly connected with an engine of a working vehicle like a tractor and a travelling-output shaft drivingly connected with rear wheels. The two shafts are disposed in parallel to each other. It is a combination of previous first speed-changing arrangement which can appear three ranges of high-speed advancing, low-speed advancing and reversing and subsequent second speed-changing arrangement which can appear multi-speed stages in every range of first speed-changing arrangement. The first and second speed-changing arrangement are disposed in front and rear of a vehicle body, thereby causing the transmission as a whole to be longitudinally long. If a clutch device for creeping-speed range is additionally provided, the length is increased even further.
If the first and second speed-changing arrangement are disposed in parallel or overlap in a longitudinal direction, the transmission can be longitudinally shortened, thereby compacting the vehicle. Also, the front-wheel driving PTO unit can be disposed further forward so as to approach the front-wheel driving unit, thereby improving efficiency of front-wheel driving.
Referring to shift patterns of the speed-changing levers described in Japanese Patent No. Hei 5-26686, a lever for operating the first speed-changing arrangement is shifted along a straight slot, and a lever for operating the second speed-changing arrangement is shifted along an H-like shaped slot. However, the second speed-changing arrangement for multi-speed-changing is used rather frequently when travelling, thereby requiring it to be operable more simply.